Today while crossing the road I witnessed a rather uncommon road event known as a ‘shockwave traffic jam’. This occours when one car slows down for whatever reason, slowing the car behind it, slowing the car behind the second car and the car behind that one and so on and so forth. This eventually spawns this mass of stopped cars that moves backwards along the road at about 20kph. It moves like a shockwave hence it’s name. This is really well shown in an experiment set up by Japanese scientists below.